Each of Patent Literatures 1 to 4 discloses a skeletal structure used in a backrest of a rear seat of a vehicle seat.
Each of these skeletal structures includes a panel formed of a substantially rectangular metal plate and a frame joined and mounted on the panel. The frame is formed of a pipe material provided along an outer edge of the panel.
The region without the frame on the panel of the skeletal structure includes a plurality of beads formed of metal plate bulging into ridge shapes and is reinforced by the beads.